Cytotoxicity of a Ti(IV) compound is independent of serum proteins.

Titanium(IV) compounds are excellent anticancer drug candidates, but they have yet to find success in clinical applications. A major limitation in developing further compounds has been a general lack of understanding of the mechanism governing their bioactivity. To determine factors necessary for bioactivity, we tested the cytotoxicity of different ligand compounds in conjunction with speciation studies and mass spectrometry bioavailability measurements. These studies demonstrated that the Ti(IV) compound of N,N'-di(o-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) is cytotoxic to A549 lung cancer cells, unlike those of citrate and naphthalene-2,3-diolate. Although serum proteins are implicated in the activity of Ti(IV) compounds, we found that these interactions do not play a role in [TiO(HBED)](-) activity. Subsequent compound characterization revealed ligand properties necessary for activity. These findings establish the importance of the ligand in the bioactivity of Ti(IV) compounds, provides insights for developing next-generation Ti(IV) anticancer compounds, and reveal [TiO(HBED)](-) as a unique candidate anticancer compound.